Meltdown and Spectre are two new levels of security vulnerability. Although most of the work depends from Intel and its microcode, there are changes that need to be done in motherboard vendors' UEFI code. However it looks like ASUS, Gigabyte and MSI are already working on BIOS updates.
All three companies have lists available of motherboards that will receive security-related BIOS updates. According to the lists, the three manufacturers will be issuing updates for motherboards based on Intel's LGA 1151, LGA 2011v3 and LGA 2066 sockets. In other words motherboards using 100-series, 200-series, 300-series, X299 and X99 chipsets.
Although the list is pretty wide, it's possible that your motherboard is not being updated even if it falls in the categories above. Not all the updates will be available at same time, if you will not see an update for your motherboard we suggest to wait a little further. According to Intel, the company will update every processor in the last five years and we should see updates for older motherboards as well.
Source:
ASUS -
Gigabyte -
MSI